1. Field of the Invention
This invention relates to a tandem rolling control system for controlling rolling speed in each stand of a hot or cold tandem rolling mill.
2. Description of the Prior Art
A typical one of conventional systems of the type as described above is illustrated in FIG. 1. Referring to FIG. 1, reference numeral 1 designates a rolling mill of a No. N stand, 2 another rolling mill of a No. N+1 stand, 3 a work or material to be rolled (this advances in a direction from the No. N to the No. N+1 stand), and 4 an electric motor for driving rolls of each of the rolling mills. In this arrangement, a variable speed electric motor is employed as the motor for the No. N stand.
Further, reference numeral 5 designates a detector for detecting a rotational speed of the electric motor (in FIG. 1, the detector is indicated by PG; a pilot generator), 6 a rolling speed controlling device, 9 a rolling load detector, and 10 a tension control device.
Now, operations of the system will be described.
In conventional tandem rolling technique, a good result of rolling is attained by controlling interstand tension either to a predetermined value or to zero.
This controlling method is described below.
Rolling torque is indirectly determined by calculating torque generated by the motor from a voltage, a current and a rotational frequency of the motor.
Referring to FIG. 2, reference numeral 1 designates a rolling mill in a No. N stand, 2 another rolling mill in a No. N+1 stand, and 3 a work or material to be rolled. (The work 3 advances in a direction from the No. N to the No. N+1 stand.)
In the system shown, a following equation stands EQU G=aF-bT (1)
where F is a rolling force, G rolling torque, T tension, a torque arm length and b tension arm length.
After the work has been bit into by the No. N stand and before it is bit into by the No. N+1 stand, EQU Go=aFo EQU .thrfore.a=Go/Fo (2)
Further, after the work has been bit into the No. N+1 stand, a following equation stands EQU G=aF-bT (3)
Accordingly, from the equations (2) and (3) above, interstand tension T is given by a following equation EQU T=(1/b)(Go/Fo.multidot.F-G)
As apparent from the foregoing description, interstand tension T can be detected from the torque Go generated by the motor (=rolling torque) and the rolling force Fo after the work has been bit into by the No. N stand and before it is bit into by the No. N+1 stand, and the torque G generated by the motor and the rolling force F after the work has been bit into by the No. N+1 stand.
Thus, it has been a practice that, during tandem rolling, a No. N stand rolling speed correcting reference is produced from a tension control device so as to control the interstand tension T to an aimed value.
A conventional tandem rolling control employs a tension controlling method using a tension control device. According to this method, interstand tension is indirectly determined from a voltage, a current and a speed of an electric motor in this way, and hence accuracy in detection is low. Besides it is disadvantageous in that controlling responsiveness to a disturbance such as a skid mark and so on is so low that a slip scar may possibly be caused to appear on a work or material to be rolled.